Stat Formula Tweak

bonus = d * d + 2 * d - 2

STC:
LLR: 2.94 (-2.94,2.94) [0.00,4.00]
Total: 99444 W: 18274 L: 17778 D: 63392

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 89757 W: 12285 L: 11896 D: 65576

bench: 8276130

src/search.cpp

@@ -1159,7 +1159,7 @@ namespace {
              && !pos.captured_piece_type()
              && is_ok((ss-1)->currentMove))
     {
-        Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
+        Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + 2 * depth / ONE_PLY - 2);
         if ((ss-2)->counterMoves)
             (ss-2)->counterMoves->update(pos.piece_on(prevSq), prevSq, bonus);
 
@@ -1439,7 +1439,7 @@ namespace {
         ss->killers[0] = move;
     }
 
-    Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
+    Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + 2 * depth / ONE_PLY - 2);
 
     Square prevSq = to_sq((ss-1)->currentMove);
     CounterMoveStats* cmh  = (ss-1)->counterMoves;
@@ -1480,13 +1480,13 @@ namespace {
     if ((ss-1)->moveCount == 1 && !pos.captured_piece_type())
     {
         if ((ss-2)->counterMoves)
-            (ss-2)->counterMoves->update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY);
+            (ss-2)->counterMoves->update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY - 1);
 
         if ((ss-3)->counterMoves)
-            (ss-3)->counterMoves->update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY);
+            (ss-3)->counterMoves->update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY - 1);
 
         if ((ss-5)->counterMoves)
-            (ss-5)->counterMoves->update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY);
+            (ss-5)->counterMoves->update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY - 1);
     }
   }